Hall effect seat belt tension sensor

ABSTRACT

A hall effect seat belt tension sensor for a vehicle. The sensor has a housing mounted to a seat belt. An anchor plate is mounted between the seat belt and a fixed point on a vehicle. The anchor plate is partially mounted in housing. A spring is mounted between the housing and the anchor plate. Tension on the seat belt causes the anchor plate to move relative to the housing. A magnetic field generator is mounted to the anchor plate. The magnetic field generator moves as the anchor plate moves. A magnetic field sensor is mounted to the housing. The sensor generates an electrical signal in response to movement of the magnetic field generator.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to the following U.S. patentapplications:

[0002] U.S. patent application Ser. No. 09/923,151 filed Aug. 6, 2001and titled, “Seat Belt Tension Sensor”.

[0003] U.S. patent application Ser. No. 09/884,615 filed Jun. 19, 2001and titled, “Seat Belt Tension Sensor with Overload Protection”.

[0004] U.S. Pat. No. 6,209,915, issued Apr. 3, 2001 and titled, “SeatBelt Tension Sensor”.

[0005] U.S. Pat. No. 6,211,668, titled, “Magnetic position sensor havingopposed tapered magnets”.

[0006] The foregoing patents have the same assignee as the instantapplication and are herein incorporated by reference in their entiretyfor related and supportive teachings.

BACKGROUND

[0007] 1. Field of the Invention

[0008] This invention relates to an automobile sensor for detecting themagnitude of a tensile force in a seat belt used in a car seat, and inparticular to a sensor that can detect the magnitude of tension in aseat belt and provide an electrical signal that is representative of themagnitude of tensile force.

[0009] 2. Description of the Related Art

[0010] Air bags have been heralded for their ability to reduce injuriesand save lives. However, since their incorporation into automobiles, aproblem has existed with people of smaller size and small children. Airbags are designed to cushion the impact of occupants and thus reduce theinjuries suffered. However, the force needed to properly cushion theoccupant varies based on the size and position of the person.

[0011] For example, a larger person requires the bag to inflate fasterand thus with more force. A smaller person may be injured by a baginflating at this higher inflation force. A smaller person is morelikely to be sitting close to the dashboard and would therefore stand ahigher chance of being injured by the impact of the inflating bag, asopposed to the passenger hitting the fully inflated bag to absorb theimpact of the accident. An average-sized person can also be injured byan airbag inflation if they are leaning forward, as for example, if theyare adjusting the radio.

[0012] Because of the concern over injury to passengers in thesesituations, the National Highway Transportation Safety Administration(or NHTSA), an administrative agency of the United States, isinstituting rules under FMVSS 208 requiring the air bag deploymentsystem to identify the passenger size and position and inflate the airbag accordingly.

[0013] One way to accomplish this task is to use a seat belt tensionsensor in conjunction with an occupant weight sensor. The weight sensorcan provide an indication of the force placed by an occupant on theseat. However, if the seat belt is unduly tightened, it can place anadditional downward force on the passenger, creating an erroneous weightreading. Similarly, it is common for infant car seats to be securedtightly to the seat. In this circumstance, it is critical for the systemto recognize that the passenger does not warrant inflation of the airbag. By sensing the tension on the seat belt in addition to the weightreading from the seat, the actual weight of the occupant can bedetermined. This allows for the system to safely deploy the air bag.

SUMMARY

[0014] It is a feature of the present invention to provide a hall effectseat belt tension sensor for attachment between a seat belt and avehicle.

[0015] Another feature of the invention is to provide a seat belttension sensor that includes a housing mounted to a seat belt. An anchorplate is mounted between the seat belt and a fixed point on a vehicle.The anchor plate is partially mounted in housing. A spring is mountedbetween the housing and the anchor plate. Tension on the seat beltcauses the spring to be compressed and the anchor plate to move relativeto the housing. A magnetic field generator is mounted to the anchorplate. The magnetic field generator moves as the anchor plate moves. Amagnetic field sensor is mounted to the housing. The sensor generates anelectrical signal in response to movement of the magnetic fieldgenerator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a perspective exploded view of the preferred embodimentof a hall effect seat belt tension sensor.

[0017]FIG. 2 is an assembled view of FIG. 1.

[0018]FIG. 3 is a perspective exploded view of another embodiment of ahall effect seat belt tension sensor.

[0019]FIG. 4 is an assembled view of FIG. 3.

[0020] It is noted that the drawings of the invention are not to scale.

DETAILED DESCRIPTION

[0021] The present invention is a seat belt tension sensor. Referring toFIGS. 1 and 2, a seat belt tension sensor assembly 20 shown., Assembly20 has a housing 40 and anchor plate 60. Housing 40 is fastened betweena seat belt webbing 30 and a structural part of the vehicle such as afloor (not shown). The belt webbing 30 has an end 31, an end 32, a beltloop 33 and stitching 34 that retains end 32.

[0022] Housing 40 has a bottom portion 41, top portion 42, flange 43,hole 44, spring channel 45, posts 46 and 47, groove 48. A cavity 50 islocated within housing 40. The bottom portion 41 and top portion 42connect together and are held together by ultrasonic welding along lip41A. Housing portion 42 has a recess or narrow portion 51 on an end ofthe housing where the seat belt wraps around.

[0023] Anchor plate 60 is loosely fitted within housing 40. Anchor plate60 includes ends 61 and 62, a cutout 63, apertures 64 and 65. Arm 66extends between aperture 65 and cutout 63. A projection 67 extends fromend 62. The anchor plate 60 is located in cavity 50. Aperture 65 goesover and surrounds flange 43. A gap (not shown) is formed between flange43 and aperture 65.

[0024] Seat belt webbing 30 is attached through hole 44 and aperture 65.The end 32 of webbing 30 is routed through hole 44 and aperture 65,wrapped back onto itself forming loop 33 and sewn with stitching 34 tosecure the seat belt webbing to assembly 20.

[0025] A spring 70 is mounted in spring channel 45. One side of springchannel 45 is formed by posts 47. One end of spring 70 is mounted overprojection 67. The other end of spring 70 rests against a block 52 incavity 50.

[0026] A printed circuit board 72 is located in a carriage 90. Printedcircuit board 72 is shaped to fit around one side of flange 43. Printedcircuit board 72 has pads 74 or holes that are soldered to wires 76 ofwire harness 78. The other end of wire harness 78 has a connector 80attached. A magnetic field sensor or hall effect device 82 is mounted inprinted circuit board 72 and extends upwardly. Electronic circuitry 84,such as an integrated circuit can be attached to the printed circuitboard to amplify and filter the signal from the hall effect device 82.Circuit lines 86 connect the hall effect device to the circuitry 84 andpads 74. Printed circuit board 72 has holes 73 that fit over pins (notshown) in carriage 90 above to hold the printed circuit board inposition.

[0027] Circuit board 72 is attached to a carriage 90. The circuit board72 is attached to carriage 90 by heat staking pins (not shown) that areinserted through holes in the circuit board. The circuit board is thenencapsulated with a sealant such as silicone to protect the electroniccomponents.

[0028] The carriage 90 and circuit board 72 are mounted in cavity 50.Slots 92 mount over posts 46. The posts are then heat staked to attachcarriage 90 to housing 41. Carriage 90 has a pair of outwardly extendingwings 91 having a slot 92. A pair of rails extend upwardly and define agroove 94. A hollow ridge 95 extends upwardly between grooves 94. Slots92 fit over posts 46 to hold carriage 90 in cavity 50. Hall effectdevice 82 extends up into a slot (not shown) inside hollow ridge 95.Rails 93 and ridge 95 extend up into mortise 106 of magnet carrier 102.

[0029] A magnetic field generator or magnet assembly 100 includes amagnet carrier 102 and a magnet 110. Magnet carrier 102 has a cavity 104and a mortise 106. The magnet carrier is preferably formed from aninsulative material such as a plastic. A magnet 110 has a groove 114 andposts 111. Pole pieces 112 are mounted on each side of magnet 110. Polepieces 112 have recesses 113 that fit over posts 111. Pole pieces 112guide the flux field generated by magnet 110. Magnet 110 preferably istapered and is adapted to generate a variable magnetic field along thelength of the magnet. Details of the operation and manufacture oftapered magnet 110 can be found in U.S. Pat. No. 6,211,668 titled,“Magnetic position sensor having opposed tapered magnets”. The contentsof which are herein incorporated by reference. The magnet 110 could alsobe a non-tapered magnet or could be a magnet that has a variable fieldstrength along its length. The magnet 110 may have a variablepolarization or a variable magnetic domain alignment along its length.

[0030] Magnet assembly 100 is located in cutout 63 and rests on carriage90. Ridge 95 extends into mortise 106 and slot 114. Magnet assembly 100slides in groove 94 as the housing 40 moves relative to the anchor plate60.

[0031] Seat belt tension sensor 20 is attached to a vehicle floor orseat or other member (not shown) by a fastener 120 such as a bolt, rivetor screw. Fastener 120 goes through aperture 64 and is attached to avehicle structure or seat. The fastener shown is threaded; however,other types of fasteners would work such as a rivet.

[0032] When a tension is applied to seat belt 30, housing 40 movesrelative to the anchor plate 60 resulting in the compression of springs70. As housing 40 moves, carriage 90 and hall effect device 82 are movedrelative to magnet assembly 100 which is held fixed by fastener 120through anchor plate 60.

[0033] As the tension in the seat belt increases, housing 40 will movefurther in relation to anchor plate 60. This causes the hall effectdevice to move. The hall effect device is located adjacent to taperedmagnet 110 which travels over ridge 95. The hall effect device outputsan electrical signal that is proportional to the strength of theperpendicular magnetic field that passes through the device. Since, themagnets are tapered, the strength of the magnetic field is variablealong the length of the magnet.

[0034] Therefore, the resulting electrical output signal of the halleffect devices changes in proportion to the amount of tension in seatbelt 30. This electrical signal is processed by electronic circuitry 84and provided to an external electrical circuit by wire harness 78 to aconventional air bag controller or occupant classification module (notshown). The air bag controller can then use the seat belt tensioninformation to compute a more accurate profile of the seat occupant anduse that information to control deployment of the airbag.

[0035] Alternative Embodiment

[0036] Referring to FIGS. 3 and 4, an alternative embodiment of a seatbelt tension sensor assembly 200 shown. Assembly 200 is similar toassembly 20 except that the housing is fixed in position the anchorplate moves. Assembly 200 has a housing 40 and anchor plate 260. Housing40 is fastened between a seat belt webbing 30 and a structural part ofthe vehicle such as a floor (not shown). The belt webbing 30 has an end31, an end 32, a belt loop 33 and stitching 34 that retains end 32.

[0037] Housing 40 has a bottom portion 41, top portion 42, flange 43,hole 44, spring channel 45, posts 46 and 47, groove 48, fastener hole49. A cavity 50 is located within housing 40. The bottom portion 41 andtop portion 42 connect together and are held together by ultrasonicwelding along lip 41 A. Housing portion 42 has a recess or narrowportion 51 on an end of the housing where the seat belt wraps around.

[0038] Anchor plate 260 is loosely fitted within housing 40. Anchorplate 260 includes ends 261 and 262, a cutout 263, apertures 264 and265. Arm 266 extends between aperture 265 and cutout 263. A projection267 extends from end 262. The anchor plate 260 is located in cavity 50.Aperture 265 goes over and surrounds flange 43. A gap (not shown) isformed between flange 43 and aperture 265.

[0039] Seat belt webbing 30 is attached through aperture 264. The end 32of webbing 30 is routed through aperture 264, wrapped back onto itselfforming loop 33 and sewn with stitching 34 to secure the seat beltwebbing to assembly 20.

[0040] A spring 70 is mounted in spring channel 45. One side of springchannel 45 is formed by posts 47. One end of spring 70 is mounted overprojection 67. The other end of spring 70 rests against a block 52 incavity 50.

[0041] A printed circuit board 72 is located in carriage 90. Printedcircuit board 72 is shaped to fit around one side of flange 43. Printedcircuit board 72 has pads 74 that are soldered to wires 76 of wireharness 78. The other end of wire harness 78 has a connector 80attached. A magnetic field sensor or hall effect device 82 is mounted inprinted circuit board 72 and extends upwardly. Electronic circuitry 84,such as an integrated circuit can be attached to the printed circuitboard to amplify and filter the signal from the hall effect device 82.Circuit lines 86 connect the hall effect device to the circuitry 84 andpads 74. Printed circuit board 72 has holes 73 that fit over pins (notshown) in carriage 90 above to hold the printed circuit board inposition.

[0042] Circuit board 72 is attached to a carriage 90. The circuit board72 is attached to carriage 90 by heat staking pins (not shown) that areinserted through holes in the circuit board. The circuit board is thenencapsulated with a sealant such as silicone to protect the electroniccomponents.

[0043] Carriage 90 and circuit board 72 are mounted in cavity 50.Carriage 90 has a pair of outwardly extending wings 91 having a slot 92.A pair of rails extend upwardly and define a groove 94. A hollow ridge95 extends upwardly between grooves 94. Slots 92 fit over posts 46 tohold carriage 90 in cavity 50. Hall effect device 82 extends up into aslot (not shown) inside hollow ridge 95. Rails 93 and ridge 95 extend upinto cutout 263 of anchor plate 260.

[0044] A magnetic field generator or magnet assembly 100 includes amagnet carrier 102 and a magnet 110. Magnet carrier 102 has a cavity 104and a mortise 106. The magnet carrier is preferably formed from aninsulative material such as a plastic. A magnet 110 has a groove 114 andposts 111. Pole pieces 112 are mounted on each side of magnet 110. Polepieces 112 have recesses 113 that fit over posts 111. Pole pieces 112guide the flux field generated by magnet 110. Magnet 110 preferably istapered and is adapted to generate a variable magnetic field along thelength of the magnet. A non-tapered magnet could also be used as couldan electromagnet. Details of the operation and manufacture of taperedmagnet 110 can be found in U.S. Pat. No. 6,211,668 titled, “Magneticposition sensor having opposed tapered magnets”. The contents of whichare herein incorporated by reference.

[0045] Magnet assembly 100 is located in cutout 263 and rests oncarriage 90. Ridge 95 extends into mortise 106 and slot 114. Magnetassembly 100 slides in groove 94 as the housing 40 moves relative to theanchor plate 260.

[0046] Seat belt tension sensor 200 is attached to a vehicle floor orseat or other member (not shown) by a fastener 120 such as a bolt, rivetor screw. Fastener 120 goes through aperture 265 and hole 44 and isattached to a vehicle structure or seat. The fastener shown is threaded;however, other types of fasteners would work such as a rivet.

[0047] When a tension is applied to seat belt 30, anchor plate 260 movesrelative to housing 40 resulting in the compression of springs 70. Asanchor plate 260 moves, magnet assembly 100 is moved relative tocarriage 90 and hall effect device 82 which are held stationary byfastener 120.

[0048] As the tension in the seat belt increases, magnet 110 will bemoved. The hall effect device is located adjacent to tapered magnet 110which is inside ridge 95. The hall effect device outputs an electricalsignal that is proportional to the strength of the perpendicularmagnetic field that passes through the device. Since, the magnets aretapered, the strength of the magnetic field is variable along the lengthof the magnet.

[0049] Therefore, the resulting electrical output signal of the halleffect devices changes in proportion to the amount of tension in seatbelt 30. This electrical signal is processed by electronic circuitry 84and provided to an external electrical circuit by wire harness 78 to aconventional air bag controller or occupant classification module (notshown). The air bag controller can then use the seat belt tensioninformation to compute a more accurate profile of the seat occupant anduse that information to control deployment of the airbag.

[0050] Remarks

[0051] The seat belt tension sensor has several advantages. It allowsaccurate sensing of seat belt tension, without excessive movement of theseat belt. The seat belt tension sensor allows an airbag controller tomake better decisions as to when and how to deploy and airbag based uponmore accurate seat occupant information. In the case of a child's carseat being strapped into a car seat, the seat belt tension sensor inconjunction with a seat weight sensor allows the airbag controller toproperly compute that the seat occupant has a low weight and to preventdeployment of the airbag.

[0052] While the invention has been taught with specific reference tothese embodiments, someone skilled in the art will recognize thatchanges can be made in form and detail without departing from the spiritand the scope of the invention. The described embodiments are to beconsidered in all respects only as illustrative and not restrictive. Thescope of the invention is, therefore, indicated by the appended claimsrather than by the foregoing description. All changes which come withinthe meaning and range of equivalency of the claims are to be embracedwithin their scope.

What is claimed is:
 1. A seat belt tension sensor for attachment betweena seat belt and a vehicle structure comprising: a) a housing having acavity; b) an anchor plate having a first portion located in the cavity,the housing movable relative to the anchor plate between a firstposition and a second position; c) a magnet mounted adjacent the anchorplate, the magnet moving as the anchor plate moves; d) a sensor mountedto the housing, the sensor generating an electrical signal in responseto moving between the first and second positions, the electrical signalchanging as a function of tension on the seat belt; and e) a springlocated between the housing and the anchor plate, the spring urging thehousing toward the first position.
 2. The seat belt tension sensoraccording to claim 1, wherein the anchor plate has a cutout, the magnetmounted in the cutout.
 3. The seat belt tension sensor according toclaim 2, wherein a carriage is mounted in the housing and the magnet ismounted in a magnet carrier, the magnet carrier being slidably supportedby the carriage, the magnet carrier located in the cutout.
 4. The seatbelt tension sensor according to claim 3, wherein the magnet generates avariable magnetic field.
 5. The seat belt tension sensor according toclaim 4, wherein the magnet is tapered.
 6. The seat belt tension sensoraccording to claim 3, wherein the sensor is a hall effect device.
 7. Theseat belt tension sensor according to claim 2, wherein the anchor platehas a first and second aperture, the cutout located between theapertures.
 8. The seat belt tension sensor according to claim 7, whereina fastener passing through the second aperture and is affixed to thevehicle structure.
 9. The seat belt tension sensor according to claim 8,wherein the seat belt passes through the first aperture.
 10. The seatbelt tension sensor according to claim 3, wherein the carriage ismounted over the sensor.
 11. The seat belt tension sensor according toclaim 6, wherein a wire harness is attached to the sensor and extendsfrom the housing.
 12. A seat belt tension sensor for attachment betweena seat belt and a vehicle structure comprising: a) a housing having acavity; b) an anchor plate mounted in the cavity, the housing movablerelative to the anchor plate; c) a carriage mounted to the housing; d) amagnet mounted to the anchor plate adjacent the carriage, the magnetmoving as the anchor plate moves, the magnet further being guided by thecarriage; and e) a magnetic field sensor mounted to the housing, thesensor generating an electrical signal in response to movement betweenthe housing and the anchor plate, the electrical signal changing as afunction of tension on the seat belt.
 13. The seat belt tension sensoraccording to claim 12, wherein the housing has a flange, the flangeextending through a first aperture in the anchor plate.
 14. The seatbelt tension sensor according to claim 12, wherein a spring is locatedbetween the housing and the anchor plate.
 15. The seat belt tensionsensor according to claim 12, wherein the anchor plate has a cutout, themagnet mounted in the cutout.
 16. The seat belt tension sensor accordingto claim 15, wherein the magnet is mounted in a magnet carrier, themagnet carrier being slidably supported by the carriage.
 17. The seatbelt tension sensor according to claim 12, wherein the magnet istapered.
 18. The seat belt tension sensor according to claim 12, whereinthe magnetic field sensor is a hall effect device.
 19. The seat belttension sensor according to claim 13, wherein a fastener passes throughthe first aperture and is affixed to the vehicle structure.
 20. The seatbelt tension sensor according to claim 2, wherein the anchor plate has asecond aperture, the seat belt passing through the first aperture. 21.The seat belt tension sensor according to claim 18, wherein a printedcircuit board is mounted in the housing, the hall effect device mountedto the printed circuit board.
 22. A seat belt tension sensor comprising:a) a housing mounted to a seat belt; b) an anchor plate mounted betweenthe seat belt and a fixed point on a vehicle, the anchor plate furtherbeing partially mounted in housing; c) a spring mounted between thehousing and the anchor plate, tension on the seat belt causing thespring to be compressed and the anchor plate to move relative to thehousing; d) a magnetic field generator mounted to the anchor plate, themagnetic field generator moving as the anchor plate moves; and e) amagnetic field sensor mounted to the housing, the sensor generating anelectrical signal in response to movement of the magnetic fieldgenerator.
 23. The seat belt tension sensor according to claim 22,wherein the anchor plate has a cutout and a first and second aperture,the seat belt attached the first aperture.
 24. The seat belt tensionsensor according to claim 23, wherein a fastener is attached through thesecond aperture to the fixed point.
 25. The seat belt tension sensoraccording to claim 22, wherein the magnet is mounted in the cutout.